A location-determining receiver, such as a Global Navigation Satellite System (GNSS) receiver, can estimate the position and velocity of an object or a vehicle. The location-determining receiver may derive imprecise positions and velocities due to inaccurate clock data from one or more satellites. GNSS augmentation systems that distribute corrections for GNSS errors provide user receivers with information that enables more accurate navigation than otherwise possible. Such augmentation systems typically include clock and orbit corrections to the transmitted satellite clock and orbit information.
A GNSS augmentation system typically includes a network of receivers at known locations. These receivers transmit information to a Processing Center, where the information is combined and GNSS corrections are computed. Because each receiver in the augmentation system network typically has its own local clock that is not synchronized with the other network clocks, it is necessary to have a single time source to which all the information from the network receivers can be referenced.
Under a prior art approach, at one or more network receivers, a precise clock (typically an atomic clock external to a network receiver) is used to supply timing signals to a network receiver. Such a network receiver thus has a very stable timing reference, and that network receiver can be used as the single time source to which the information from the other network receivers can be referenced. Because of the possible failure of the precise clock or the failure of communication links between this network receiver and the Processing Center, several precise clocks are usually deployed to improve the system reliability. The performance of these precise clocks is typically evaluated and monitored in real-time to facilitate switching between precise clocks.
In practice, this prior art approach requires expensive atomic clocks to be located at several different sites with network receivers. Thus, there is a need for an improved economical method and system for determining clock corrections for a satellite navigation system. In particular, there is a need for a method and system for determining clock corrections that does not require a precise clock at any network receiver.